Electrically driven submersible pump systems are used for example on off-shore installations, or within the cargo tanks of ships used for carrying oil and bulk chemicals for example. They comprise a pump head having a pumping section including an impeller and a motor chamber containing an electric motor for driving the impeller, a pipe stack arranged to be suspended from a support with the pump head carried at the lower end of the pipe stack, the pipe stack having a discharge duct for liquid pumped by the pump and electric supply conductors for supplying power to the electric motor.
It is a disadvantage of the prior art systems of this kind that the electric power to the motor in the pump head is conveyed by means of a stiff and heavy electric cable which adds to the difficulties of raising the pump head to the support level for maintenance and inspection.
Moreover, the cable of the prior art systems has to be protected by an outer pipe particularly when explosive liquids such as crude oils with a high vapour pressure are being pumped. If the cable is merely clamped to the cargo discharge pipe in the pipe stack, the cable experiences considerable wear and tear from chemical decomposition, and from mechanical forces such as waves when it is exposed to these. The electric power cable of the prior art systems provides no means for monitoring, at the deck or support level, the performance or condition of the pump head.
It is accordingly an object of the invention to provide a pipe stack for an electrically driven submersible pump system which can be readily assembled from separable pipe stack sections.
It is also an object of the invention to provide a pipe stack section detachably connectible to like or co-operating sections which has electrical conductors extending therealong with means for insulating the conductors by dielectric liquid.
It is a further object of the invention to provide a pipe stack section having liquid insulated electrical conductors extending therealong, the section structure providing protective means around the liquid insulated conductors.
It is an additional object of the invention to provide a submersible electrically driven pump system with a pipe stack in which dielectric liquid for insulating power supply conductors to the pump motor is circulated.
It is a further object of the invention to provide a submersible pump system in which circulation of a dielectric oil for insulating electrical power supply conductors to a pump motor is employed to lubricate bearings.
It is yet another object of the invention to provide a submersible pump system in which dielectric liquid for insulating electrical power supply conductors is circulated to a pump head and is employed to monitor and/or to modify (as by cooling) pump head performance.